[FIX] website_sale: preventing list index out of range

When user enters empty space in name field instead of entering an
actual name and confirm their billing, shipping address then when
they click on paynow to confirm order they will face the issue
'list index out of range'.

Note : Do the paypal configuration before following below steps.

Steps to produce:
1) Vist the website as a public user.
2) Create a sale order by adding some products to the cart.
3) While entering shipping and billing address, in the name field enter
some space.
4) Click on next button.
5) Now a sale order is created.
6) Go to orders through 'website' module.
7) Open the order created and generate a payment link.
8) Paste that payment link in another tab or browser .
9) Click on pay
10) By following above steps you will encounter the error.

This commit will prevent the above error.

sentry - 4177783431

closes odoo/odoo#122229

Signed-off-by: Saurabh Mishra (sami) <sami@odoo.com>

addons/website_sale/controllers/main.py

@@ -725,7 +725,10 @@ class WebsiteSale(http.Controller):
 
         # error message for empty required fields
         for field_name in required_fields:
-            if not data.get(field_name):
+            val = data.get(field_name)
+            if isinstance(val, str):
+                val = val.strip()
+            if not val:
                 error[field_name] = 'missing'
 
         # email validation